1. Field of the Invention
The present invention relates to a servo information recording device (Servo Track Writer (STW)) that records servo information for positioning a head of a magnetic disk unit to a desired track and a servo information recording method. In this specification, a rotational motion with a rotation angle of less than 360° is expressed as “swing”.
2. Description of the Related Art
A positional relationship between a magnetic disk (recording medium) and an actuator (head drive section) that drives a head defined in a known typical STW is configured to be the same as that defined in a magnetic disk unit in which the magnetic disk is set.
In such a conventional STW, YAW angle, which is an angle (quantity) formed between the head swing (rotation) radial direction and disk medium rotation circumferential direction, exceeds its ideal value in at least one of the radial direction inside and outside of a servo information writing zone on the magnetic disk. Further, YAW angle greatly differs between the radial direction inside and outside of the servo information writing zone.
A cause of the above defects is that the direction of line connecting two points at which the head swinging trajectory crosses the radial direction inside and outside of the servo information writing zone on the magnetic disk is significantly displaced from the radial direction of the magnetic disk.
Writing operation of the conventional STW is performed as follows. A controller creates servo information corresponding to R-position of an actuator on one track of the disk medium by one rotation and starts writing the servo information at a constant reference phase of the disk medium (same timing for each rotation cycle).
In this case, the reference phase stays constant relative to all tracks. After completion of the writing operation corresponding to one rotation, the controller moves the actuator to the next track and repeats the same operation as above.
As a prior art relating to the present invention, there is known a configuration in which the storage surfaces of a plurality of stacked magnetic disk are divided into a plurality of concentric, circular storage zones and two magnetic heads having different arm lengths. In this configuration, two magnetic heads are switched in such a way that longer arm is used for the inner circumferential side (refer to, e.g., Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 10-208411).
In a generally known STW, YAW angle exceeds its ideal value in one of the radial direction inside and outside of the writing zone on a magnetic disk, so that a side erase phenomenon, which depends on YAW angle of a head, becomes prominent in one of the radial direction inside and outside. This side erase brings about level down of servo information. For example, in the case where servo information is written starting from the radial direction inside of the magnetic disk, the side erase phenomenon becomes strongly apparent in the servo information writing end zone (i.e., radial direction outside). On the other hand, in the case where servo information is written starting from the radial direction outside of the magnetic disk, the side erase phenomenon becomes strongly apparent in the radial direction inside.
The servo information writing zone of the STW is wider, by the amount of parts tolerance and disk eccentricity, than that used in a magnetic disk unit. Thus, YAW angle of the head of the STW correspondingly becomes large in both ends of the writing zone, with the result that the levitation margin of the head becomes smaller than that in the magnetic disk unit. It follows that the side erase of the servo information easily occurs, thus deteriorating the quality of the servo information.
Further, in the STW, in order to make the trajectory of servo information (head) recorded onto a magnetic disk corresponding to the swinging trajectory of a head of a magnetic disk unit, a distance between the disk rotation center and pivot (swing axis) and distance between the pivot and head are made corresponding to those set in the magnetic disk unit. Therefore, manufacturing of a new magnetic disk unit having a different positional configuration requires a dedicated STW and its actuator assembly facility, resulting in increased cost.
Further, in the technique of above Patent Document 1, a plurality of heads having different arm lengths need to be prepared. This increases the size and complexity of the device, also resulting in increased cost.